Outside of laboratories, microbial species rarely exist in isolation. Many important environmental processes are actually mediated by complex communities of microbes. In many cases, two or more species have evolved to perform a cooperative metabolic activity that would be energetically unfavorable for either organism acting independently. Research published in the December 3 issue of Science and led by DOE scientist Derek Lovley of the University of Massachusetts, Amherst, describes a new mechanism by which the bacterium Geobacter metallireducens consumes ethanol, an important intermediate compound in oxygen free soils and sediments, in cooperation with a second organism Geobacter sulfureducens. For this reaction to yield energy for either partner, electrons produced from ethanol oxidation must be rapidly consumed. Although it was previously assumed that the first organism uses a hydrogen production mechanism to pass electrons to its partner, the authors have discovered that electrons are instead directly fed to G. sulfureducens via conductive "nanowires" called pili on the cell surface, resulting in much more efficient collaborative growth. These results provide important new clues on the fundamentals used by microbes to mediate important environmental processes such as carbon cycling and contaminant transformation and suggest intriguing new approaches to direct generation of electricity in microbial fuel cell systems.
Reference: Summers, Z.M., H. E. Fogarty, C. Leang, A. E. Franks, N. S. Malvankar, and D. R. Lovley. 2010. "Direct Electron Exchange Within Aggregates of an Evolved Syntrophic Coculture of Anaerobic Bacteria," Science 330:1413-15.
Contact: Dan Drell, SC-23.2, (301) 903-4742
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